A NEW STUDY by Brian Richmond and David Strait of George Washington University
that scrutinized the fossilized wrist joints of two of our earliest known human ancestors,
A. afarensis (best known as “Lucy”) and A. anamensis, concluded that our earliest
known human ancestors probably walked on their knuckles in a way similar to modern
chimpanzees and gorillas.

Did Humans Evolve From Tree-Dwellers or Animals on Ground?

This discovery lends support to the theory that humans didn't
evolve from tree dwellers, but from ancestors who were already adapted to walking on
the ground.

It's All In the Wrist

The researchers compared the fossilized wrist joints from known human ancestors
with the wrist joints of other primates. The wrist anatomy of Lucy and her cousins
resembles that of chimpanzees and gorillas in having features that buttress the wrist
joint and help to lock the wrist into a stable position so that the animal can support its
weight on its fingers. It was not until the later species, A. africanus, at 2 to 3 million
years ago, that evidence of a more humanlike, flexible wrist joint exists.